Hot-rolled steel strip, floor structure, design method of floor structure, and construction method of floor structure

Abstract

To provide an H-shaped steel that can be preferably used as a structural element even when a width-thickness ratio of a web is equal to or larger than a certain value.SOLUTION: Provided is an H-shaped steel 25. A maximum strength that the H-shaped steel 25 can bear is equal to or larger than an elastic local buckling bearing force of the H-shaped steel 25. In a case where a load is applied to the H-shaped steel 25, rigidity of the H-shaped steel 25 decreases when the load becomes equal to or larger than the elastic local buckling bearing force. the H-shaped steel 25 has a function to be restored to an initial position in a case where the load is removed before the load applied to the H-shaped steel 25 reaches the maximum bearing force of the H-shaped steel 25.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to hot rolling Steel strip, floor structure manufacturing, a design method for a floor structure, and a construction method for a floor structure.

Background Art

[0002] In the small beams that support the floors of buildings, from the viewpoint of suppressing floor deflection and vibration, H-shaped steel with high flexural rigidity and flexural strength per unit mass of steel is widely used. H-shaped steel has a cross-sectional specification excellent in the second moment of area and section modulus, and the thinner the web and the thicker the flange, the higher its cross-sectional efficiency. However, H-shaped steel with thin web and flange plate thickness has poor plastic deformation performance after reaching the maximum strength, and when an unexpected local external force (for example, a local concentrated load acts due to the running of an overloaded truck) acts on the H-shaped steel, there is a risk that the H-shaped steel will break early. For this reason, in general steel frame structures, an upper limit is set for the width-thickness ratio of the plate elements constituting the H-shaped steel cross-section, and it is common to ensure the redundancy of the H-shaped steel even when an unexpected local load acts, and there is a limit to thinning the web. For example, in Patent Document 1, it is described that when the width-thickness ratio of the web is larger than a certain value (for example, 75), early local buckling may occur in the web and the plastic deformation ability may be insufficient, so it is necessary to take measures such as locally reinforcing the web.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, for an H-shaped steel with a large web thickness-to-width ratio, for example, the mass per unit length of the H-shaped steel can be reduced while maintaining the size of the sectional moment of inertia. Therefore, even if the yield strength of the H-shaped steel is sacrificed, it is also conceivable to use an H-shaped steel with a web thickness-to-width ratio greater than a certain value by taking advantage of its high rigidity as a structural element of a building.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide an H-shaped steel that can be preferably used as a structural element even when the web thickness-to-width ratio is greater than a certain value, a floor structure including the H-shaped steel, a hot-rolled steel strip used for the H-shaped steel, a design method for the floor structure, and a construction method for the floor structure.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention proposes the following means. In the H-shaped steel of the present invention, when the Young's modulus of the material used for the H-shaped steel is E and the yield strength of the material is σ y when the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, elastic local buckling occurs in the H-shaped steel and the rigidity of the H-shaped steel decreases, and when the load is less than the maximum yield strength that the member can withstand, the H-shaped steel elastically recovers when the load is removed.

[0007] According to the present invention, when the width-to-thickness ratio of the web is relatively large and an external force acts on a building due to natural disasters such as earthquakes and winds or disturbances such as the passage of vehicles inside the building, if the load acting on the H-shaped steel exceeds the elastic local buckling resistance, elastic local buckling occurs in this H-shaped steel and the rigidity of the H-shaped steel decreases. When a larger external force acts on the building, redistribution of the load inside the building is caused, and the load concentration on the H-shaped steel is alleviated. As a result, for example, the force is transmitted to other beams adjacent to the H-shaped steel. Thereby, it is possible to alleviate the concentration of the load on a specific H-shaped steel, for example, to promote the load redistribution in a building in which H-shaped steel is used, and to prevent a situation where a load unexpectedly large for a designer acts on an H-shaped steel with an extremely large web width-to-thickness ratio having poor plastic deformation performance and leads to the destruction of the H-shaped steel. When the acting load is less than the maximum bearing capacity of the H-shaped steel, when the load is removed, the H-shaped steel elastically returns to its initial state. Therefore, it is possible to maintain the same function against natural disasters such as earthquakes that occur repeatedly without causing serious structural damage to the H-shaped steel, and the H-shaped steel can be preferably used as a structural element over a long period of time.

[0008] Further, the floor structure design method of the present invention is a floor structure design method for designing a floor structure including an H-shaped steel used as a beam, a support beam, and a floor slab joined to the H-shaped steel and the support beam respectively. When the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, local buckling occurs in the H-shaped steel and the rigidity of the H-shaped steel is reduced, so that at least a part of the load is designed to be transmitted to the support beam through the floor slab. When the load decreases to less than the elastic local buckling resistance, the H-shaped steel is designed to return to its initial position. Moreover, the construction method of the floor structure of the present invention is a construction method of a floor structure including an H-shaped steel used as a beam, a support beam, and a floor slab joined to the H-shaped steel and the support beam respectively. When the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, local buckling occurs in the H-shaped steel and the rigidity of the H-shaped steel is reduced, so that at least a part of the load is transmitted to the support beam through the floor slab during construction. When the load decreases to less than the elastic local buckling resistance, the H-shaped steel is constructed to be restored to the initial position, which is a feature of this method.

[0009] According to these inventions, when the width-thickness ratio of the web is relatively large and the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance, local buckling occurs in the H-shaped steel and the rigidity of the H-shaped steel is reduced, so that at least a part of this load acts on the support beam through the floor slab in the design (construction). Therefore, for example, it is possible to promote load redistribution in a building where H-shaped steel is used and prevent a relatively large load from acting on the H-shaped steel. And when the acting load is reduced to less than the elastic local buckling resistance, the H-shaped steel elastically recovers. For this reason, it is possible to maintain the same function against natural disasters such as earthquakes that occur repeatedly without causing serious structural damage to the H-shaped steel, and the H-shaped steel can be preferably used as a structural element over a long period of time.

[0010] In addition, in the H-shaped steel, the H-shaped steel includes a web and a pair of flanges arranged so as to sandwich the web. By satisfying equation (1), when the magnitude of the load acting on the H-shaped steel among the loads is equal to or greater than the elastic local buckling resistance, the ratio of the load acting on the H-shaped steel among the loads is reduced compared to the case where the magnitude of the load acting on the H-shaped steel among the loads is smaller than the elastic local buckling resistance. When the load is removed before the magnitude of the load acting on the H-shaped steel reaches the maximum bearing capacity of the H-shaped steel, the H-shaped steel may be designed to be restored to the initial state without causing serious structural damage. However, E: Young's modulus of the H-shaped steel, σ y : Yield strength of the H-shaped steel, b w : Width of the web, t w : Thickness of the web, b f : Width of the pair of flanges, t f : Thickness of the pair of flanges.

[0011]

Equation

[0012] According to the present invention, as a result of intensive studies, the inventors have found the following. That is, when the H-shaped steel satisfies the left inequality in Equation (1) and the load is equal to or greater than the elastic local buckling resistance, the maximum load-bearing capacity of the H-shaped steel will inevitably be a member specification that exceeds the elastic local buckling resistance. When a load acts on the H-shaped steel, the H-shaped steel exhibits the effect of elastic local buckling and reducing rigidity. When the load decreases before reaching the maximum load-bearing capacity, the H-shaped steel can return to its initial state (position) without significant structural damage. And when the H-shaped steel satisfies the right inequality in Equation (1), the deflection occurring at the center of the web can be made 3 mm or less, which is equal to or less than that of the current H-shaped steel for building structures. Therefore, the risk that local deformation of the web due to thinning impairs workability can be eliminated.

[0013] Further, in the H-shaped steel, the H-shaped steel includes the web and a pair of flanges arranged so as to sandwich the web. By satisfying Equation (2), when the load is equal to or greater than the elastic local buckling resistance, the ratio of the load acting on the H-shaped steel among the loads can be reduced, and when the load is less than the elastic local buckling resistance, it may elastically recover when the load is removed. However, E: Young's modulus of the H-shaped steel, σ y : Yield strength of the H-shaped steel, t w : Thickness of the web, b f : Width of the pair of flanges, t f : Thickness of the pair of flanges.

[0014]

Number

[0015] According to the present invention, as a result of intensive studies, the inventors have found the following. That is, when the H-shaped steel satisfies the left inequality in the formula (2) and the load is equal to or greater than the elastic local buckling resistance, the maximum resistance of the H-shaped steel will always be a member specification that exceeds the elastic local buckling resistance. When a load acts on the H-shaped steel, the H-shaped steel exhibits the effect of elastic local buckling and reducing rigidity, and when the load decreases before reaching the maximum resistance, the H-shaped steel can be restored to its initial state without significant structural damage. And when the H-shaped steel satisfies the right inequality in the formula (2), by making the flange thickness equal to or greater than the web thickness, the sectional performance such as the sectional moment of inertia of the H-shaped steel can be improved. For example, when the H-shaped steel is a welded fabricated H-shaped steel, when welding the web to the flange, it is possible to prevent the flange from being completely melted in its thickness direction and forming holes in the flange.

[0016] Further, in the H-shaped steel, the H-shaped steel may be a secondary beam. According to the present invention, it is possible to provide a secondary beam that can be preferably used as a structural element even when the width-thickness ratio of the web is greater than a certain value.

[0017] Further, in the H-shaped steel, the H-shaped steel may be a welded fabricated H-shaped steel in which the web and a pair of flanges are welded to each other. According to the present invention, it is possible to provide a welded fabricated H-shaped steel that can be preferably used as a structural element even when the width-thickness ratio of the web is greater than a certain value.

[0018] Further, in the H-shaped steel, the yield strength σ y of the H-shaped steel may be 235 MPa or more and 1000 MPa or less. According to the present invention, it can correspond to the yield strength σ y of general H-shaped steel.

[0019] Furthermore, the hot-rolled steel strip of the present invention is characterized in that it is used for the web or a pair of flanges of an H-shaped steel which is a welded and assembled H-shaped steel as described in any one of the above. According to the present invention, it is possible to provide a hot-rolled steel strip used for the web or a pair of flanges of an H-shaped steel which is a welded and assembled H-shaped steel and can be preferably used as a structural element even if the width-thickness ratio of the web is larger than a certain value.

[0020] Moreover, the floor structure of the present invention includes the H-shaped steel as described in any one of the above, and a floor slab supported from below by the upper flange of the H-shaped steel and joined to the upper flange, and is characterized in that the movement of the upper flange in the direction along the horizontal plane is restricted by the floor slab. According to the present invention, in the floor structure, the movement of the upper flange in the direction along the horizontal plane is restricted by the floor slab. Therefore, for example, it is possible to suppress the elastic local buckling of the H-shaped steel.

[0021] Another floor structure of the present invention includes the H-shaped steel as described in any one of the above, and a support member joined or in contact with at least one of a pair of flanges of the H-shaped steel at at least one end in the material axis direction of the H-shaped steel, and is characterized in that a compressive force or a tensile force of the H-shaped steel is transmitted between the at least one end of the H-shaped steel and the support member. According to the present invention, in the floor structure, a compressive force or a tensile force is transmitted from the support member to at least one of a pair of flanges at at least one end of the H-shaped steel. Therefore, the H-shaped steel can be used as a structural element that can withstand a compressive force or a tensile force.

Advantages of the Invention

[0022] According to the hot-rolled steel strip, H-shaped steel, floor structure, design method of the floor structure, and construction method of the floor structure of the present invention, even if the width-thickness ratio of the web is larger than a certain value, the H-shaped steel can be preferably used as a structural element.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0024] Hereinafter, an embodiment of a hot-rolled steel strip, an H-shaped steel, a floor structure, a design method of the floor structure, and a construction method of the floor structure according to the present invention will be described with reference to FIGS. 1 to 9. In the following, the design method of the floor structure is simply referred to as the design method, and the construction method of the floor structure is simply referred to as the construction method.

[0025] 〔1. Configuration of Hot-Rolled Steel Strip, H-Shaped Steel, and Floor Structure〕 As shown in FIG. 1, the floor structure 2 is used for the building 1. In FIG. 1, the floor slab 35 described later is shown by a two-dot chain line. As shown in FIGS. 1 and 2, the floor structure 2 includes a plurality of column members 10, a plurality of large beams (support members) 15, a plurality of small beams which are H-shaped steels 25, and a floor slab 35. Note that the floor structure 2 may not include a plurality of column members 10. The floor structure 2 may further not include a plurality of main girders 15 or H-shaped steels 25.

[0026] The plurality of column members 10 are made of steel frame, RC (Reinforced Concrete), SRC (Steel Reinforced Concrete), CFT (Concrete Filled steel Tube), etc. For example, the plurality of column members 10 extend along the vertical direction. The plurality of column members 10 are arranged at the intersections of a plurality of straight lines forming a lattice (in a lattice shape) in plan view. For example, the main girder 15 is made of H-shaped steel. The main girder 15 extends in a direction along the horizontal plane. The main girder 15 has a first web 16, a first upper flange 17, and a first lower flange 18. The plurality of main girders 15 are erected on the plurality of column members 10. The plurality of main girders 15 are arranged in a frame shape in plan view and surround a predetermined area. A gusset plate 19 is joined to the first web 16 etc. of the main girder 15 by welding or the like (see FIG. 2).

[0027] The H-shaped steel 25 is a welded fabricated H-shaped steel. The H-shaped steel 25 extends in the material axis direction of the H-shaped steel 25 along the horizontal plane. The H-shaped steel 25 has a second web (web) 26, a second upper flange (flange, upper flange) 27, and a second lower flange (flange) 28. As shown in FIG. 2, the second web 26 is formed in a flat plate shape presenting a rectangle when viewed in the thickness direction of the second web 26. The second web 26 is arranged such that the thickness direction of the second web 26 is along the horizontal plane. The flanges 27, 28 are formed in flat plate shapes and are respectively arranged such that the thickness directions of the flanges 27, 28 are along the vertical direction. The second lower flange 28 is arranged below the second upper flange 27. The flanges 27, 28 are arranged so as to sandwich the second web 26 in the vertical direction. The second web 26 connects the center in the width direction on the lower surface of the second upper flange 27 and the center in the width direction on the upper surface of the second lower flange 28.

[0028] The second web 26 and / or flanges 27, 28 configured as described above are made of a hot-rolled steel strip (a strip made of a hot-rolled steel plate), not shown in the drawings.

[0029] The plurality of H-shaped steels 25 are used in the building 1. The H-shaped steel 25 is manufactured by welding the second web 26 and the flanges 27, 28, which are individually manufactured in advance, to each other. As shown in FIGS. 1 and 2, the plurality of H-shaped steels 25 are provided inside (within the area surrounded by the plurality of main girders 15) surrounded by the plurality of main girders 15. The plurality of H-shaped steels 25 are arranged side by side with a space therebetween. Both ends of the plurality of H-shaped steels 25 are installed on the plurality of main girders 15. The plurality of H-shaped steels 25 are pin-jointed to the plurality of main girders 15. Specifically, as shown in FIG. 2, the second web 26 of the H-shaped steel 25 and the gusset plate 19 are joined to each other by a fastening member 29 including high-strength bolts or the like. The second upper flange 27 abuts against the first upper flange 17 of the main girder 15 from the side of the first upper flange 17 and is in contact therewith. The second lower flange 28 is disposed above the first lower flange 18 of the main girder 15. That is, at both ends of the H-shaped steel 25 in the material axis direction, the second upper flange 27 is in contact with the first upper flange 17 of the main girder 15.

[0030] Note that, at one end of the H-shaped steel 25 in the material axis direction, the second upper flange 27 may be in contact with the first upper flange 17 of the main girder 15. Not only the second upper flange 27 but also the second lower flange 28 may be in contact with the first lower flange 18 of the main girder 15. The second upper flange 27 may be joined to the first upper flange 17 of the main girder 15 by welding or the like.

[0031] Here, as shown in FIG. 3, the dimensions and the like in a cross section orthogonal to the material axis direction of the H-shaped steel 25 are defined. Note that, for the units of length and the like described below, SI units such as "m" for length are preferably used. Let the thickness of the second web 26 be t wIt is defined as follows. The width of the second web 26 (the length in the direction orthogonal to the thickness direction of the second web 26 and the material axis direction) is defined as b w It is defined as follows. The thickness of the flanges 27 and 28 is defined as t f It is defined as follows. The width of the flanges 27 and 28 (the length in the direction orthogonal to the thickness direction of the flanges 27 and 28 and the material axis direction) is defined as b f It is defined as follows. The Young's modulus of the H-beam 25 (the second web 26 and the flanges 27 and 28) is defined as E. The yield strength of the H-beam 25 is defined as σ y It is defined as follows. The width-to-thickness ratio of the second web 26 (b w / t w ) is 4.4√(E / σ y ) or more. The width-to-thickness ratio of the second web 26 is more preferably 5.3√(E / σ y ) or more. For example, the width-to-thickness ratio of the second web 26 is 200 or less. The yield strength σ y of the H-beam 25 is 235 MPa (megapascal) or more and 1000 MPa or less.

[0032] Hereinafter, among the plurality of H-beams 25, the H-beam 25 closest to where the load (concentrated load) acts may be referred to as the H-beam 25A. Among the plurality of H-beams 25, those other than the H-beam 25A may be referred to as the H-beam (support beam) 25B.

[0033] As shown in FIG. 2, the floor slab 35 is provided above the plurality of main girders 15 and the plurality of H-beams 25. The floor slab 35 is supported from below by the first upper flanges 17 of the plurality of main girders 15 and the second upper flanges 27 of the plurality of H-beams 25. In the present embodiment, the floor slab 35 is a deck composite slab. The floor slab 35 includes a deck plate 36, concrete 37, reinforcing bars 38, and shear connectors 39. The deck plate 36 is formed by bending a steel plate or the like. The deck plate 36 is disposed on the first upper flanges 17 of the main girders 15 and the second upper flanges 27 of the H-beams 25, respectively. The concrete 37 is formed in a flat plate shape with the thickness direction along the vertical direction. The concrete 37 is disposed on the deck plate 36.

[0034] The floor slab 35 includes a plurality of reinforcing bars 38. A first reinforcing bar 38a, which is part of the plurality of reinforcing bars 38, extends along a certain H-shaped steel 25 among the plurality of H-shaped steels 25. The remaining second reinforcing bars 38b of the plurality of reinforcing bars 38 extend in a direction orthogonal to the first reinforcing bar 38a. The first reinforcing bar 38a and the second reinforcing bars 38b are embedded in the concrete 37. For example, the shear connector 39 is a stud with a head. The floor slab 35 includes a plurality of shear connectors 39. The lower ends of the plurality of shear connectors 39 are fixed to the upper surfaces of the first upper flange 17 of the girder 15 and the second upper flange 27 of the H-shaped steel 25 with a space therebetween. The shear connector 39 is embedded in the concrete 37 through the deck plate 36. As described above, the floor slab 35 is joined to the first upper flange 17 and the second upper flange 27. Then, the movement of the first upper flange 17 and the second upper flange 27 in the direction along the horizontal plane is restricted by the floor slab 35.

[0035] Note that in the floor structure 2 configured as described above, the compressive force or tensile force of the H-shaped steel 25 is transmitted between both end portions in the material axis direction of the H-shaped steel 25 and the girder 15.

[0036] 〔2. Examination of the relationship between the cross-sectional shape of the H-shaped steel and the load-bearing capacity of the H-shaped steel〕 Hereinafter, the results of examining the relationship between the cross-sectional shape such as the width-to-thickness ratio of the H-shaped steel 25A and the elastic local buckling load-bearing capacity (load threshold value) and the maximum load-bearing capacity of the H-shaped steel 25A will be described. Note that hereinafter, the second web 26 may sometimes be simply referred to as the web 26. Similarly, the second upper flange 27 may sometimes be simply referred to as the upper flange 27, the second lower flange 28 may sometimes be simply referred to as the lower flange 28, and the H-shaped steel 25A may sometimes be simply referred to as the H-shaped steel 25.

[0037] 〔2.1. Effect of rigidity reduction due to elastic local buckling〕 Figure 4 shows an overview of the analysis model of the H-section steel 25. The axis along the material axis direction of the H-section steel 25 is defined as the Y-axis. The axis along the thickness of the web 26 is defined as the X-axis. The axes along the thicknesses of the flanges 27 and 28 are defined as the Z-axis. The analysis conditions were set as follows. · The cross-sectional shape orthogonal to the Y-axis of the H-section steel 25 was set as H-700×175×3.2×4.5. · Assuming that four-point bending acts on the H-section steel 25, after applying the boundary conditions as shown in Figure 4 considering its symmetry, an elastoplastic analysis was performed in which a forced deformation in the Z-axis direction was applied to the web (A in the figure). · It was assumed that the movement in the direction along the horizontal plane of the upper flange 27 (the direction along the X-axis in Figure 4) was restrained by the floor slab 35.

[0038] Using the analysis model, a large deformation elastoplastic analysis by the finite element method (FEM) was performed. Figure 5 shows the analysis results. In Figure 5, the horizontal axis represents the vertical displacement (mm) at the end of the H-section steel 25, and the vertical axis represents the load (kN) acting on the H-section steel 25. In Figure 5, the analysis results are shown by the solid line L1. The line obtained by extending the initial stiffness of the analysis results is shown by the dotted line L2. On the vertical axis, the bending moment F1 causes a compressive stress degree in the H-section steel 25 to reach the elastic local buckling resistance σ cr when the bending moment F cr is shown. The elastic local buckling resistance σ cr is an eigenvalue obtained from the buckling eigenvalue analysis, and the bending moment F cr is the value obtained by multiplying the elastic local buckling resistance σ cr by the section modulus of the H-section steel.

[0039] Based on Figure 5, the relationship between the displacement of the H-section steel 25 with respect to the load (bending moment F1) was confirmed. When the bending moment F1 acts on the H-section steel 25, when the bending moment F1 reaches the elastic local buckling resistance F cr (when the bending moment F1 reaches the elastic local buckling resistance F crWhen it reaches the above, the rigidity of the H-shaped steel 25 decreases (refer to the region R1 in Fig. 5). However, as the load continues to increase thereafter, the yield strength (bending moment F1) of the H-shaped steel 25 increases, and it can be confirmed that the bending moment F1 reaches the maximum yield strength F max The maximum yield strength F max means the maximum value of the yield strength that the H-shaped steel 25 can withstand. In this way, the maximum yield strength F max that the H-shaped steel 25 can bear is lower than the elastic local buckling strength F cr (the maximum yield strength F max is greater than or equal to the elastic local buckling strength F cr ). The H-shaped steel 25 with such specifications is used. Then, when the bending moment F1 acts on the H-shaped steel 25, it becomes possible to surely decrease the bending rigidity of the H-shaped steel 25 before reaching the maximum yield strength F max

[0040] 〔2.2. Limitation of the lower limit value of the width-to-thickness ratio of the H-shaped steel where the elastic local buckling strength is smaller than the maximum yield strength〕 Analyze the lower limit value of the width-to-thickness ratio of the web 26 and the flanges 27, 28 for which the effect of 〔2.1〕 is exerted. The analysis was carried out under the following conditions. · The height of the H-shaped steel 25 was set to 700 mm. · The widths of the H-shaped steel 25 were set to four types: 175 mm, 350 mm, 525 mm, and 700 mm. · The thickness t f of the flanges 27, 28 was set to six types: 3.2 mm, 4.5 mm, 6 mm, 9 mm, 12 mm, and 16 mm. · The thickness t w of the web 26 was set to four types: 3.2 mm, 4.5 mm, 6 mm, and 9 mm. Note that the thickness t f of the flanges 27, 28 was made thicker than the thickness t w of the web 26. · The yield strength σ y of the H-shaped steel 25 was set to 235 MPa, 295 MPa, 325 MPa, 385 MPa, 440 MPa, and 500 MPa. · It was assumed that an equal bending moment acts on the H-shaped steel 25.

[0041] Among the obtained analysis results, the maximum endurance F max exceeds the elastic local buckling endurance σ cr The analysis cases are shown in Fig. 6. In Fig. 6, the horizontal axis represents the square root of the value obtained by dividing the material strength (yield strength) σ y of the web 26 by the elastic local buckling endurance σ cr_web of the web 26 (√(σ y / σ cr_web )) (hereinafter referred to as the generalized width-thickness ratio of the web). The material strength σ y means the 0.2% offset (0.2% endurance according to JIS Z 2241) obtained from the tensile test of the material. The vertical axis represents the square root of the value obtained by dividing the material strength σ y of the flanges 27, 28 by the elastic local buckling endurance σ cr_flange of the flanges 27, 28 (√(σ y / σ cr_flange )) (hereinafter referred to as the generalized width-thickness ratio of the flange). The elastic local buckling endurance σ cr_web and the elastic local buckling endurance σ cr_flange are the values obtained by equations (3) and (4). However, ν is the Poisson's ratio of the H-shaped steel 25.

[0042]

Equation

[0043] Among the obtained analysis results, the analysis cases where the maximum endurance F max is less than the elastic local buckling endurance F cr are shown in Fig. 7. The horizontal axis and the vertical axis of Fig. 7 are the same as those of Fig. 6, respectively.

[0044] From Fig. 6, it can be seen that the analysis results where the maximum endurance F max exceeds the elastic local buckling endurance F cr exist in the region where the generalized width-thickness ratio of the web is 0.94 or more, or the generalized width-thickness ratio of the flange is 1.46 or more. Also, when considering Fig. 7 together, when the generalized width-thickness ratio of the web becomes 1.15 or more, or the generalized width-thickness ratio of the flange becomes 1.46 or more, the maximum endurance F maxis surely greater than the elastic local buckling resistance F cr It was found that the analysis result is obtained.

[0045] Here, considering that the Young's modulus E of the steel material is 205000 N / mm 2 , and the Poisson's ratio ν is 0.3, substituting the formula (4) and the physical property values of the steel material into the generalized width-thickness ratio of the web and calculating, the maximum bearing capacity F max is greater than the elastic local buckling resistance F cr . As shown in the formula (5), the lower limit value of the generalized width-thickness ratio of the web for this purpose can be transformed into the formula of the width-thickness ratio (b w / t w ) of the web 26.

[0046]

Equation

[0047] Considering that the Young's modulus E of the steel material is 205000 N / mm 2 , and the Poisson's ratio ν is 0.3, substituting the formula (3) and the physical property values of the steel material into the generalized width-thickness ratio of the web and calculating, the maximum bearing capacity F max is greater than the elastic local buckling resistance F cr . As shown in the formula (6), the lower limit value of the generalized width-thickness ratio of the flange for this purpose can be transformed into the formula of the width-thickness ratio (b f / t f ) of the flanges 27, 28.

[0048]

Equation

[0049] By satisfying the formula (5) or (6), when the load acting on the H-section steel 25A is equal to or greater than the elastic local buckling resistance F cr , the ratio of the load acting on the H-section steel 25A among the said loads is reduced, and when this load is removed, the H-section steel 25A can be restored to the initial state (initial position) without causing significant structural damage. That is, for the H-section steel 25A, when the load acting on the H-section steel 25A is the maximum bearing capacity F of the H-section steel 25Amax When unloaded before reaching [a certain value], the H-shaped steel 25A has a restoring function (function) to restore to its initial state.

[0050] In this case, when the load acting on the H-shaped steel 25A is greater than or equal to the elastic local buckling resistance σ cr If it is, since the plate elements constituting the member cross-section deform in the out-of-plane direction due to the elastic local buckling of the H-shaped steel 25A, the stress distribution within the cross-section becomes non-uniform, stress redistribution within the cross-section occurs, and the bending stiffness of the entire member decreases. Then, it promotes the load redistribution within the building 1 to prevent damage to the H-shaped steel 25A. These stiffness decreases are caused by the elastic local buckling of the H-shaped steel 25, not by the member yielding of the H-shaped steel 25. Therefore, when the load acting on the H-shaped steel 25A is removed, the H-shaped steel 25A restores to its initial state without significant structural damage.

[0051] 〔2.3. Upper Limit of Web Depth-to-Thickness Ratio〕 Subsequently, an analysis was conducted on the upper limit of the web depth-to-thickness ratio. The web 26 has initial deflections due to welding assembly. According to the previous literature 1 (JIS G 3353:2011 Welded Lightweight H-Shaped Steel for General Structures), in welded lightweight H-shaped steel, the maximum value of the out-of-plane deflection occurring in the web is controlled to be 2 mm or less during manufacturing. Therefore, it is considered that in welded H-shaped steel, deflections of up to about 2 mm are generated due to welding assembly. Considering that the self-weight of the upper flange 27 or the lower flange 28 acts on the web 26 with the initial deflections caused by this welding assembly, the initial deflections (deflections) of the web 26 will become even larger.

[0052] Therefore, for example, if the web 26 is made extremely thin, there is a problem that the web 26 cannot support the self-weight of the upper flange 27 or the lower flange 28, and it becomes difficult to maintain the shape of the H-shaped steel 25. Therefore, the dimensions of the web 26 and the flanges 27, 28 were changed as follows. · Width b of the flanges 27, 28 fwas changed at 100 mm intervals between 100 mm and 1000 mm. · The width b of the web 26 w was changed at 100 mm intervals between 100 mm and 1000 mm. · The thickness t of the web 26 w , and the thickness t of the flanges 27, 28 f were changed in 16 ways, which are 0.4 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.6 mm, 2.3 mm, 3.2 mm, 4.5 mm, 6 mm, 9 mm, 12 mm, 16 mm, 19 mm, 22 mm, 25 mm, 28 mm. When the dimensions were changed as described above, the cross-sectional specifications of the H-shaped steel 25 in which the deflection of the web 26 exceeded 3 mm were investigated.

[0053] In the prior literature 2 (JIS G 3192:2014 Shapes, Dimensions, Masses and Tolerances of Hot-Rolled Sections), out-of-plane shape irregularities of the web of a member having an H-shaped cross-section are allowed up to 3 mm. Considering this, when the self-weight of the upper flange 27 or the lower flange 28 acts on the H-shaped steel 25 (web 26) in which an initial deflection (= 2 mm) has occurred due to welded assembly, the member specifications in which the out-of-plane deformation of the web 26 becomes 3 mm or less were investigated.

[0054] Fig. 8 shows an overview of the models considered. In this study, the conditions were set as follows. · The web 26 is regarded as an infinitely long plate element simply supported at both upper and lower ends. · The initial deflection of the web 26 was designated as δ1. · Assuming a load condition in which the self-weight F3 of the flanges 27, 28 acts on the ends of the web 26, the cross-sectional shape of the H-shaped steel 25 in which the deflection δ2 generated at the center of the web 26 becomes larger than 3 mm was examined.

[0055] Fig. 9 shows the investigation results. In Fig. 9, the horizontal axis represents the width-thickness ratio of the web 26, and the vertical axis represents the value of (b f t f / (b w t w )) (b f t f / (bw t w The value of ) represents the ratio of the areas of the flanges 27 and 28 to the area of the web 26 (hereinafter referred to as the area ratio). The results indicated by the ○ marks in Fig. 9 are cases where the deflection δ2 of the web 26 in the out-of-plane direction is greater than 3 mm. The results indicated by the · marks are cases where the deflection δ2 of the web 26 in the out-of-plane direction is 3 mm or less. As a result of the investigation, it was found that for the condition where the deflection of the web 26 becomes greater than 3 mm, the threshold value can be evaluated by using the relationship of the area ratio. The curve L4 in Fig. 9 satisfies the equation (7-1). For the H-shaped steel 25 corresponding to the region where the width-to-thickness ratio of the web 26 is smaller than that of the curve L4, that is, f t f / (b w t w if the value of ) is smaller than that of the curve L4, it was found that the deflection δ2 generated at the center of the web 26 becomes 3 mm or less. When the above conditions are applied to the equation (7-1) and the equation is transformed, the equation (7-2) is obtained.

[0056]

Equation

[0057] 〔2.4. Upper Limit of Width-to-Thickness Ratio of Flange〕 Generally, for reasons such as enhancing the cross-sectional performance of the H-shaped steel 25, the thickness t f of the flanges 27 and 28 is w equal to or greater than the thickness t of the web 26. From this condition, the equation (8) is obtained.

[0058]

Equation

[0059] In addition, from the equations (5) and (7-2), the equation (9) for the width-to-thickness ratio of the web 26 is obtained. From the equations (6) and (8), the equation (10) for the width-to-thickness ratio of the flanges 27 and 28 is obtained. When the H-shaped steel 25 satisfies the formula (9) or (10), and the load acting on the H-shaped steel 25A is unloaded before reaching the maximum bearing capacity F of the H-shaped steel 25A, the H-shaped steel 25 has the above-mentioned restoration function. max In the case where the load acting on the H-shaped steel 25A is unloaded before reaching the maximum bearing capacity F of the H-shaped steel 25A, the H-shaped steel 25 has the above-mentioned restoration function.

[0060]

Number

[0061] In the design method (construction method) of this embodiment, when the load acting on the H-shaped steel 25A is equal to or greater than the elastic local buckling bearing capacity F cr , elastic local buckling occurs in the H-shaped steel 25A, and the rigidity of the H-shaped steel 25A is reduced, so that at least a part of the load is transmitted to the H-shaped steel 25B through the floor slab 35 for design (construction). Then, when the load acting on the H-shaped steel 25A is removed, the H-shaped steel 25A is designed (constructed) to restore to the initial state without significant structural damage. cr In the case where the load acting on the H-shaped steel 25A is equal to or greater than the elastic local buckling bearing capacity F cr , elastic local buckling occurs in the H-shaped steel 25A, and the rigidity of the H-shaped steel 25A is reduced, so that at least a part of the load is transmitted to the H-shaped steel 25B through the floor slab 35 for design (construction). Then, when the load acting on the H-shaped steel 25A is removed, the H-shaped steel 25A is designed (constructed) to restore to the initial state without significant structural damage.

[0062] As described above, in the H-shaped steel 25 of this embodiment, when the width-thickness ratio of the second web 26 is relatively large, that is, 5.3√(E / σ y ) or more, elastic local buckling occurs in the H-shaped steel 25A, and the rigidity of the H-shaped steel 25A is reduced, so that at least a part of this load acts on the H-shaped steel 25B. Therefore, it is possible to promote the load redistribution in the building 1 where the H-shaped steel 25A is used and prevent the load from concentrating extremely on the H-shaped steel 25. y As described above, in the H-shaped steel 25 of this embodiment, when the width-thickness ratio of the second web 26 is relatively large, that is, 5.3√(E / σ y ) or more, elastic local buckling occurs in the H-shaped steel 25A, and the rigidity of the H-shaped steel 25A is reduced, so that at least a part of this load acts on the H-shaped steel 25B. Therefore, it is possible to promote the load redistribution in the building 1 where the H-shaped steel 25A is used and prevent the load from concentrating extremely on the H-shaped steel 25. And when the load acting on the H-shaped steel 25A does not exceed the maximum bearing capacity of the H-shaped steel 25A, when the load is removed, the H-shaped steel 25A restores to the initial state without significant structural damage. In this way, even when a load that causes the member rigidity of the H-shaped steel 25A to decrease acts, after the load is removed, the member restores to the initial state. Therefore, the effect of the present invention can be continuously maintained against the repeatedly occurring seismic forces, and the H-shaped steel 25A can be preferably used as a structural element.

[0063] The H-shaped steel 25A satisfies equation (9). As a result of intensive studies by the inventors, the following has been found. That is, when the load acting on the H-shaped steel 25A satisfies the left inequality in equation (9) and is greater than or equal to the elastic local buckling resistance F cr or more, before the H-shaped steel 25A reaches the maximum load-bearing capacity F max elastic local buckling occurs in the H-shaped steel 25A, reducing the rigidity of the H-shaped steel 25A. When the load acting on the H-shaped steel 25A is removed before reaching the maximum load-bearing capacity of the H-shaped steel 25A, the H-shaped steel 25A can be restored to its initial state without significant structural damage. And when the H-shaped steel 25A satisfies the right inequality in equation (9), the deflection occurring at the center of the second web 26 can be made 3 mm or less, which is equal to or less than that of the existing H-shaped steel for building structures. Therefore, the risk that the local deformation of the second web 26 due to thinning impairs workability can be eliminated.

[0064] The H-shaped steel 25 satisfies equation (10). As a result of intensive studies by the inventors, the following has been found. That is, when the load acting on the H-shaped steel 25A satisfies the left inequality in equation (10) and is greater than or equal to the elastic local buckling resistance F cr or more, before the H-shaped steel 25 reaches the maximum load-bearing capacity F max elastic local buckling occurs in the H-shaped steel 25A, reducing the rigidity of the H-shaped steel 25A. When the load acting on the H-shaped steel 25A is removed before reaching the maximum load-bearing capacity of the H-shaped steel 25A, it can be restored to its initial state without significant structural damage. And when the H-shaped steel 25A satisfies the right inequality in equation (10), the thickness of the flanges 27, 28 can be made equal to or greater than the thickness of the second web 26, improving the cross-sectional performance such as the second moment of area of the H-shaped steel 25A. When the H-shaped steel 25A is a welded fabricated H-shaped steel, when welding the second web 26 to the flanges 27, 28, it is possible to prevent the flanges 27, 28 from being completely melted in the thickness direction and having holes.

[0065] The H-shaped steel 25A is a secondary beam. Therefore, even if the width-to-thickness ratio of the second web 26 is greater than a certain value, it is possible to provide a secondary beam that can be preferably used as a structural element. The H-shaped steel 25A is a welded fabricated H-shaped steel. For this reason, even if the width-to-thickness ratio of the second web 26 is greater than a certain value, it is possible to provide a welded fabricated H-shaped steel that can be preferably used as a structural element.

[0066] The yield strength σ of the H-shaped steel 25A y is 235 MPa or more and 1000 MPa or less. Thus, it can correspond to the yield strength σ of a general H-shaped steel 25A. y Further, the hot-rolled steel strip of the present embodiment is used for the second web 26 or the flanges 27, 28 of the H-shaped steel 25 which is a welded fabricated H-shaped steel. Therefore, even if the width-to-thickness ratio of the second web 26 is greater than a certain value, it is possible to provide a hot-rolled steel strip used for the second web 26 or the flanges 27, 28 of the H-shaped steel 25 which is a welded fabricated H-shaped steel and can be preferably used as a structural element.

[0067] The floor structure 2 includes the H-shaped steel 25A and the floor slab 35. In the floor structure 2, the movement of the second upper flange 27 in the direction along the horizontal plane is restrained by the floor slab 35. For this reason, for example, buckling of the H-shaped steel 25A can be suppressed. The floor structure 2 includes the H-shaped steel 25A and the main beam 15. In the floor structure 2, a compressive force or a tensile force is transmitted from the main beam 15 to the second upper flange 27 at both ends of the H-shaped steel 25A. For this reason, the H-shaped steel 25A can be used as a structural element that can withstand a compressive force or a tensile force.

[0068] Also, in the design method and the design method of the present embodiment, when the width-to-thickness ratio of the second web 26 is relatively large, i.e., 5.3√(E / σ y ) or more, the load acting on the H-shaped steel 25A is the elastic local buckling resistance F cr ​In the case described above, when elastic local buckling occurs in the HEA 25A and the rigidity of the HEA 25A is reduced, at least a part of this load is designed (constructed) to act on the HEA 25B via the floor slab 35. Therefore, for example, it is possible to promote load redistribution within the building 1 where the HEA 25A is used, and prevent a large load from concentrating on the HEA 25A due to local concentrated loads. And when the load acting on the HEA 25A is removed before the load borne by the HEA 25A reaches the maximum allowable stress of the HEA 25A, the HEA 25A will return to its initial state without significant structural damage. Therefore, against natural disasters such as earthquakes that occur repeatedly, the effect of load redistribution due to the reduction in rigidity of the HEA 25A according to the present invention can be continuously exerted, and the HEA 25A can be preferably used as a structural element.

[0069] As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes configuration changes, combinations, deletions, etc. within the scope not departing from the gist of the present invention. For example, in the above embodiment, the HEA 25 does not necessarily satisfy equations (9) and (10). The HEA 25 may be a rolled HEA instead of a welded fabricated HEA. The HEA 25 may be a main beam instead of a secondary beam. In this case, the supporting member is the column member 10. The yield strength σ of the HEA 25 y may be less than 235 MPa or may exceed 1000 MPa.

Description of reference numerals

[0070] Two - floor structure 15 Main beam (supporting member) 25, 25A HEA (secondary beam) 25B HEA (supporting beam) 26 Second web (web) 27 Second upper flange (flange, upper flange) 28 Second lower flange (flange)

Claims

1. An H-shaped steel, a floor slab supported from below by an upper flange of the H-shaped steel and joined to the upper flange, comprising: wherein the maximum load-bearing capacity of the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, when a load acts on the H-shaped steel, when the load becomes equal to or greater than the elastic local buckling resistance, the H-shaped steel buckles and the rigidity of the H-shaped steel decreases, and at least a part of the load acts on a support beam joined to the H-shaped steel via the floor slab through the floor slab, thereby reducing the proportion of the load acting on the H-shaped steel, when the load acting on the H-shaped steel is unloaded before reaching the maximum load-bearing capacity of the H-shaped steel, the H-shaped steel has a function of restoring to the initial position of the H-shaped steel before the load acts on the H-shaped steel, a floor structure in which movement of the upper flange in a direction along the horizontal plane is restricted by the floor slab.

2. An H-shaped steel, a floor slab supported from below by an upper flange of the H-shaped steel and joined to the upper flange, comprising: wherein the H-shaped steel has a web, and a pair of flanges arranged so as to sandwich the web, comprising: by satisfying equation (1), the maximum load-bearing capacity of the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, when a load acts on the H-shaped steel, when the load becomes equal to or greater than the elastic local buckling resistance, the H-shaped steel buckles and the rigidity of the H-shaped steel decreases, and at least a part of the load acts on a support beam joined to the H-shaped steel via the floor slab through the floor slab, thereby reducing the proportion of the load acting on the H-shaped steel, when the load acting on the H-shaped steel is unloaded before reaching the maximum load-bearing capacity of the H-shaped steel, the H-shaped steel has a function of restoring to the initial position of the H-shaped steel before the load acts on the H-shaped steel, a floor structure in which movement of the upper flange in a direction along the horizontal plane is restricted by the floor slab. However, E: Young's modulus of the H-shaped steel, σ ｙ : Yield strength of the H-shaped steel, b ｗ : Width of the web, t ｗ : Thickness of the web, b ｆ : Width of the pair of flanges, t ｆ : Thickness of the pair of flanges. 【Number 1】

3. An H-shaped steel, a floor slab supported from below by an upper flange of the H-shaped steel and joined to the upper flange, comprising: wherein the H-shaped steel has a web, and a pair of flanges arranged so as to sandwich the web, comprising: By satisfying the formula (2), when a load acts on the H-shaped steel, if the load becomes equal to or greater than the elastic local buckling resistance of the H-shaped steel, the H-shaped steel buckles and the rigidity of the H-shaped steel decreases, and at least a part of the load acts on a support beam joined to the H-shaped steel via the floor slab through the floor slab, thereby reducing the ratio of the load acting on the H-shaped steel. When the load acting on the H-shaped steel is unloaded before reaching the maximum resistance of the H-shaped steel, the H-shaped steel has a function of restoring to the initial position of the H-shaped steel before the load acts on the H-shaped steel. A floor structure in which movement of the upper flange in a direction along the horizontal plane is restricted by the floor slab. However, E: Young's modulus of the H-shaped steel, σ ｙ : Yield strength of the H-shaped steel, t ｗ : Thickness of the web, b ｆ : Width of the pair of flanges, t ｆ : Thickness of the pair of flanges. 【Number 2】

4. The floor structure according to any one of claims 1 to 3, wherein the H-shaped steel is a secondary beam.

5. The floor structure according to any one of claims 1 to 4, wherein the H-shaped steel is a welded fabricated H-shaped steel in which a web and a pair of flanges are welded to each other.

6. The yield strength σ of the H-shaped steel ｙ is 235 MPa or more and 1000 MPa or less, and the floor structure according to any one of claims 1 to 5.

7. A hot-rolled steel strip used for a web or a pair of flanges of an H-shaped steel, which is a welded fabricated H-shaped steel according to any one of claims 1 to 6.

8. At least one end in the material axis direction of the H-shaped steel is provided with a support member joined or in contact with at least one of a pair of flanges of the H-shaped steel. The floor structure according to any one of claims 1 to 6, wherein a compressive force or a tensile force of the H-shaped steel is transmitted between the at least one end of the H-shaped steel and the support member.

9. An H-shaped steel, A support beam, A floor slab joined to the H-shaped steel and the support beam respectively, A floor structure design method for designing a floor structure including: When the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, the H-shaped steel buckles and the rigidity of the H-shaped steel decreases, and at least a part of the load acts on the support beam through the floor slab, so as to design to reduce the ratio of the load acting on the H-shaped steel, and When the load is less than the elastic local buckling resistance, when the load is removed, the H-shaped steel is designed to restore to the initial position of the H-shaped steel before the load acts on the H-shaped steel.

10. An H-shaped steel, A support beam, A floor slab joined to the H-shaped steel and the support beam respectively, A floor structure construction method for constructing a floor structure including: When the load acting on the H-shaped steel is equal to or greater than the elastic local buckling resistance of the H-shaped steel, the H-shaped steel buckles and the rigidity of the H-shaped steel decreases. At least a part of the load acts on the support beam through the floor slab, so that the construction is carried out to reduce the proportion of the load acting on the H-shaped steel, and When the load is less than the elastic local buckling resistance, when the load is removed, the H-shaped steel is constructed to restore to the initial position of the H-shaped steel before the load acts on the H-shaped steel. A construction method of a floor structure.

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